1. Field of the Invention
The invention relates in general to an airbag trigger control system, and more particularly to an airbag trigger control system suitable for appropriately triggering an airbag system for protecting occupants in a vehicle upon collision of the vehicle.
2. Description of Related Art
A known example of the conventional airbag trigger control system is disclosed in J-PA-11-286257. The disclosed airbag trigger control system includes a floor sensor disposed in a floor tunnel of a vehicle body. The floor sensor is operable to output a signal corresponding to an impact exerted to the floor tunnel. The airbag trigger control system is arranged to obtain control parameters on the basis of the output signals generated from the floor sensor and to control a trigger of the airbag system such that the airbag system is triggered when the obtained control parameters exceed a predetermined threshold value. In addition, the airbag trigger control system includes satellite sensors disposed in a front of the vehicle body, which are operable to generate output signals corresponding to the impact exerted to the front of the vehicle body. The airbag trigger control system is arranged to detect a magnitude of the impact exerted to the front of the vehicle body on the basis of the output signals generated from the satellite sensors, while being arranged to change the predetermined threshold value depending upon the detected magnitude of the impact, such that the threshold value decreases as the magnitude of the detected impact increases. Namely, the airbag becomes more likely to deploy as the magnitude of the impact exerted to the front of the vehicle body increases. Thus, the conventional airbag trigger control system is able to appropriately trigger the airbag system for protecting the occupants in the vehicle.
In the case where the satellite sensors become unavailable to properly output the signals corresponding to the impact exerted to the vehicle body, the threshold value used for the trigger control of the airbag system should not be determined on the basis of the output signals generated from the satellite sensors. In this case, the threshold value has to be changed to other threshold value for abnormal conditions so that the airbag system is appropriately triggered irrespective of the magnitude of the impact exerted to the front of the vehicle body.
One kind of the satellite sensor is capable of outputting a predetermined abnormality determination signal to an electronic control unit, upon detection of an abnormal state of the sensor. Thus, the airbag trigger control system with such satellite sensors is capable of determining whether the satellite sensors are in the abnormal condition. This facilitates determination of whether the threshold value used for triggering the airbag should be changed to a given value as the threshold value for the abnormal conditions.
In this respect, the threshold value for abnormal conditions is required to be selected in the following conditions: (a) the satellite sensors are incapable of generating abnormality determination signals due to drop in the supply voltage or the like; (b) the output signals corresponding to the impact exerted to the vehicle body are not applied from the satellite sensors to the electronic control unit due to disconnection of a signal line therebetween, or due to short-circuit occurred in the signal lines; and (c) the electronic control unit receives the signal that takes an unusual form which cannot be identified as the one corresponding to the impact exerted to the vehicle body. In the aforementioned conditions, however, it is not possible to determine the abnormal state of the satellite sensors on the basis of the abnormality determination signals generated thereby. The conventional airbag trigger control system does not take account at all of the needs for changing the threshold value for triggering the airbag to the given value as the threshold value for the abnormal conditions as indicated above.